Heat exchanger and metthod for manufacturing thereof

ABSTRACT

A heat exchanger ( 1 ) comprising two sets of medium through-flow channels (P,S) through which two media can flow in heat-exchanging contact; walls ( 2 ) separating the channels; heat conducting fins ( 3 - 8 ) arranged on both sides of each wall ( 2 ), wherein a fin on the one side of a wall is in thermal contact with a similar contact surface of a fin on the other side of this wall; wherein the wall ( 2 ) are embodied as membrane and the fins ( 3 - 8 ) are embodied as heat transferring strips with a general wave shape and are provided with contact surfaces connected to the walls and main planes extending between two wall.

The invention relates to a heat exchanger, comprising

two sets of medium through-flow channels which are placed mutuallyinterlaced and through which two media can flow physically separatedfrom each other in a primary circuit (P) respectively a secondarycircuit (S) and solely in heat-exchanging contact;

walls separating said channels;

heat-conducting fins which are arranged on both sides of each wall,which fins extend with their main planes in the respective flowdirections of said media, wherein a fin on the one side of a wall, via acontact surface in the main plane of the wall in question and formingpart of the fin, is in thermal contact with a similar contact surface ofa fin on the other side of this wall;

a housing in which the channel-bounding walls with the fins areaccommodated, to which housing two inlets and two outlets for the twosets of channels connect either individually per channel or commonly forthe sets of channels via respective manifolds.

Such a heat exchanger is known in many embodiments. It is an object ofthe invention to embody a heat exchanger such that it is very light andcan be manufactured inexpensively, while nevertheless still having anexcellent efficiency.

In this respect the heat exchanger according to the invention has thefeature that the walls are embodied as membranes and the fins areembodied as heat-transferring, for instance metal strips with a generalwave shape, which fins are provided with contact surfaces connected tothe walls and main planes extending between two walls, this such that,in addition to a thermal function, the fins also have a structuralfunction, wherein the coefficient of heat transfer of the wholeseparating wall amounts to a minimum of 1 W/m²K.

The heat exchanger according to the invention thus derives itsmechanical strength and rigidity substantially from the fins. Accordingto the prior art the mechanical strength and rigidity of heat exchangersare not generally determined by fins but by the heat-exchanging walls.This requires the use of mechanically strong and therefore thick walls,which thereby have the inherent drawback of a greater thermalresistance, to the extent the same materials are used.

The heat exchanger according to the invention can combine a highefficiency with a very compact construction.

It should be understood that at least in theoretical sense a membrane isan “infinitely thin” skin-like element, which has a negligible bendingstiffness and can therefore only derive its stiffness from the fact thatit is clamped on its ends, optionally in combination with a certaintensile stress in the form of a bias. When a pressure difference occursbetween the primary circuit and the secondary circuit, a certain bendingof a practical membrane cannot be wholly prevented. This means that thepressure resistance of a heat exchanger according to the invention islimited to a value determined by the mechanical properties, such as thethickness of the foil used, the tensile strength, the ability tostretch, the limit of stretch, the bias, the mutual distance between thefoil layers and the like. When a bias is used, this forms an extra loadon the foil material. The maximum tensile stress in the foil istherefore equal to the total maximal tensile stress minus the bias.

In order to make the heat transfer between the layers of fins as greatas possible, the embodiment is recommended in which correspondingcontact surfaces are in thermal contact via the wall.

In a practical embodiment the heat exchanger has the feature that thecontact surfaces are adhered to the wall by means of an adhesive layerapplied to at least one contact surface.

An alternative has the feature that corresponding contact surfaces aredirectly connected to each other via a perforation in the wall by meansof an adhesive layer applied to at least one contact surface.

It will be apparent that it is essential that the thermal resistanceformed by the foil wall and the glue layer must be as small as possible.In this respect these layers must be thin.

In respect of the thermal contact between adjacent layers of fins, theembodiment is recommended in which the walls consist of PVC and the finsare connected to the walls by an ultrasonic treatment or a thermaltreatment, in combination with pressure. The connection can for instancetake place by welding, soldering or the like, in any case such that thethermal resistance formed by the foil is absent.

A preferred embodiment has the special feature that the housing isform-retaining and the walls are connected to the housing in mannerresistant to tensile stress, such that the tensile stresses occurring inthe walls as a result of a pressure difference between the two sets ofchannels can be absorbed by the housing.

Another embodiment has the feature that the walls are biased such that,at a preselected maximum permissible pressure difference between the twosets of medium through-flow channels, the bending of the wall betweenthe free space defined by the contact surfaces of the fins, i.e. thebending of the membrane occurring at the relevant pressure divided bythe relevant mutual distance between the contact surfaces in question,amounts to a maximum of 2.5%.

In the embodiment in which corresponding contact surfaces are in thermalcontact via the foil wall, the heat exchanger preferably has the featurethat the thermal resistance of the foil transversely of its main planeamounts to a maximum of 0.1 of the thermal resistance in the case ofdirect contact between contact surfaces directed toward each other, andis therefore negligible.

The heat exchanger preferably has the feature that the thermalresistance of the foil in its main plane over the mutual distancebetween two fins adjoining in flow direction is at least 10 timesgreater than in the case of fins directly coupled to each otherthermally.

A practical embodiment has the special feature that the walls consist ofPET, for instance reinforced PET, are treated with a corona discharge,are then provided with a primer, followed by a glue layer for connectionto the contact surfaces of the fins.

An alternative embodiment has the feature that the walls consist of PVCand that the fins are connected to the walls by an ultrasonic treatmentor a thermal treatment, in combination with pressure.

A substantial improvement in the tensile strength relative to the usualfoil materials is obtained with a heat exchanger which has the featurethat the foil consists of a fibre-reinforced material, which fibresconsist for instance of glass, boron, carbon. The fibres can forinstance be embodied as fabric or as non-woven.

A great improvement of the thermal conductivity of the foil is realizedwith a heat exchanger which has the feature that the walls consist of aplastic in which aluminium powder is embedded.

In order to enable the heat exchanger to be maintenance-free and make itsuitable for the most diverse applications, the heat exchanger can havethe feature that the walls consist of PET, for instance reinforced PET,are treated with a corona discharge, are then provided with a primer,followed by a glue layer for connection to the contact surfaces of thefins.

A very practical embodiment has the special feature that the wallsprotrude outside the fins such that they can be connected to a frame,for instance in order to place them under bias, or such that theprotruding wall parts can be thermally formed into interlacing units andmanifolds for respectively joining together and separating again thesets of channels. This embodiment alleviates the problem of embodying aninterlacing unit and manifold on both sides of the heat exchanger.

A determined embodiment has the feature that the heat exchanger is givena modular structure with blocks which can be releasably coupled to eachother. Thus is achieved that the heat exchanger can be manufactured indifferent dimensions by making use of blocks, without substantialchange-over of a production line being necessary for this purpose.

A particular embodiment has the feature that the layers are ordered inthe sequence P, S, P, S, P, S and so on.

Another embodiment has the feature that the layers are ordered in thesequence P, P, S, S, P, P and so on.

In order to limit the mechanical load on the foil layers as much aspossible during production of the heat exchanger, a preferred embodimenthas the special feature that the contact surfaces of the fins haverounded peripheral edges.

In an embodiment in which the foil consists of a fibre-reinforcedmaterial, the heat exchanger can have the special feature that thefibres have an anisotropic heat conduction, such as carbon fibres,wherein the heat conduction is smaller in the main plane of the foilthan in transverse direction thereof. The tensile strength of the foilstrips and thereby the pressure resistance of the heat exchanger ishereby substantially improved, and a very good heat contact betweenadjacent fins is also achieved.

A suitable choice of the foil materials can be made with an eye tooperating conditions and applications. Thermoplastic plastics as well asthermosets such as polyether imide are suitable. The foil materials canalso be provided with a coating, for instance of another plastic, asilicon material or the like. In the case of fibre reinforcement thefibres can have diameters of a few μm.

Another choice of material for the membranes is metal, in particular aplastic foil with a metal coating on at least one of the two sides.

A very simple solution to a possibly occurring corrosion problemconsists of the adhesion having taken place with an anticorrosivecoating applied to at least one of the two contact surfaces and forinstance comprising a primer layer and/or an adhesive layer extendingover the whole surface of the fins and optionally the wall.

A specific embodiment has the special feature that the adhesive layer isof the type which can be thermally activated and that the fins areadhered to the relevant wall and/or to an adjacent set of fins at theposition of the contact surfaces by heating and pressure by means of aheated pressing punch.

In yet another variant the heat exchanger has the feature that the finsare provided on the side remote from said coating with a second coatingwhich can withstand said heating and pressure.

The invention will now be elucidated with reference to the annexeddrawings. Herein:

FIG. 1 shows a perspective partial view of a heat exchanger according tothe invention, wherein the housing is not shown for the sake of clarity;

FIG. 2 a shows a schematic perspective view on small scale of a heatexchanger according to the invention with a housing and interlacingunits and manifolds;

FIG. 2 b shows the detail II of FIG. 2 a on a larger scale;

FIG. 3 is a schematic representation of an alternative offsetarrangement of the fins;

FIG. 4 is a schematic representation of an unreinforced membrane;

FIG. 5 shows a partly broken away perspective view of a membranereinforced with a fibre fabric;

FIG. 6 shows a view corresponding with FIG. 5 of a membrane reinforcedwith a non-woven material;

FIGS. 7 a and 7 b show respective phases of adhesion of the contactsurfaces of fins to a membrane;

FIG. 8 shows an alternative method of adhesion;

FIG. 9 a shows a cross-section corresponding with FIG. 8 of analternative form;

FIG. 9 b is a perspective view of the preliminary stage of the structureaccording to FIG. 9 a;

FIG. 10 a and 10 b show views corresponding with FIGS. 7 a and 7 brespectively of an embodiment in which the fins are coupled directly toeach other via holes in the membrane;

FIG. 10 c is a perspective view of the phase shown in FIG. 10 a andcorresponding with FIG. 9 b;

FIG. 11 shows the preliminary stage of an embodiment in which themembrane is provided on both sides with an adhesive layer;

FIG. 12 is a view corresponding with FIG. 11 of an embodiment in whichthe contact surfaces of the fins are provided with a coating;

FIG. 13 a shows a highly schematic view of a device for manufacturing aheat exchanger according to the invention in industrial manner;

FIG. 13 b shows detail XIII of FIG. 13 a on enlarged scale;

FIG. 13 c shows a perspective view in slightly further developed anddetailed form of the device of FIG. 13 a;

FIG. 14 shows a cross-sectional view of a part of a heat exchangeraccording to the invention during the production stage, wherein themembranes are fixed under tensile stress by means of tensioning means;

FIG. 15 shows a front view of a heat exchanger, wherein the fins and themedium circuits are ordered in a first arrangement;

FIG. 16 shows a view corresponding with FIG. 15, wherein the fins andthe medium circuits are ordered in a second arrangement; and

FIG. 17 shows a cross-sectional view of alternative tensioning means.

FIG. 1 shows a heat exchanger 1, comprising a number of layers of foil2, between which extend respective strips 3, 4, 5, 6, 7, 8 and so on.These strips 3-8 form heat-conducting fins and are manufactured for thispurpose from for instance copper. By means of means to be describedhereinbelow the fins are adhered with their mutually facing contactsurfaces to foils 2 on either side of these foils 2. In this embodimentthe successive foil layers alternately bound a primary and a secondarycircuit, designated in the figure with arrows P and S respectively.These medium circuits relate to the flow of media for placing inheat-exchanging contact with each other, for instance gaseous media,liquid media or respectively gas and liquid or two-phase media.

The drawing further shows that strips 3, 4, 5 have a limited length inthe medium flow direction and that the subsequent fin strips 6, 7, 8 areplaced at a distance. This enhances the effective heat transfer. Theintermediate space 9, which is not provided with fins, acts effectivelyas thermal separation in the transport direction. A prerequisite hereforis that the foil material has a limited heat conductivity and is forinstance not manufactured from a good heat-conducting material such ascopper. Plastic is for instance a very suitable choice. Because thefoils are embodied as membranes and are therefore very thin, theypresent only a negligible thermal resistance at the position of theheat-transferring contact surfaces of the fins directed toward eachother.

FIG. 2 shows a heat exchanger 10 which is constructed on the basis ofthe above described membrane-fin-heat exchanger, wherein use is made ofa housing. Connecting to the free ends are respective interlacing unitsand manifolds 12 for P in, 13 for P out, 14 for S in and 15 for S out.

FIG. 2 b shows the interior of heat exchanger 10. This is essentiallythe same unit as in FIG. 1 and is therefore also designated withreference numeral 1.

FIG. 3 shows very schematically an alternative arrangement of fins inrespective strips 16, 17, 18, 19, 20, 16. It will be apparent that thefins are offset ⅕ the pitch distance at a time in transverse directionrelative to flow direction 21. The front edge of each fin is herebyalways situated in a practically undisturbed flow. This enhances theheat transfer.

FIG. 4 shows a membrane 22 schematically.

FIG. 5 shows a membrane 23 which is reinforced with a fabric 24, forinstance consisting of glass fibre, carbon fibre or the like. It isnoted that the drawing is not to scale and that a mat 24 of this typecan also be impregnated with a plastic, whereby the fabric ismedium-tight and can moreover melt, for instance through heat, foradhering to the contact surfaces of the fins.

FIG. 6 shows a membrane 25 with a non-woven reinforcement 26.

FIG. 7 a shows a membrane 28 with glue layers 29 at the position ofcontact surfaces 30 of fins 31. The structure drawn in FIG. 7 b isobtained by pressing, wherein the glue is pressed out slightly into sidezones 32. The glue 29 can be pre-heated or be of the pressure-sensitivetype.

FIG. 8 shows an embodiment wherein fins 31 are pressed into foil 28during heating and under pressure. The foil material is hereby madethinner in the intermediate zone 33 and the material is pressed slightlyoutward at the side in zones 34. This embodiment is favourable in thesense that a good seal is always ensured, while the already thin foilmaterial is made extra-thin.

FIG. 9 a shows a variant in which fins 35, 36 are provided withcomplementary corrugations 37, 38 respectively. A good positioning ofthe contact surfaces is hereby always ensured. The corrugations 37, 38also extend in transverse direction. This aspect is clearly shown inFIG. 9 b. Arrows 39 indicate that fins 35, 36 are forced together duringheating and under pressure when foil 28 is compressed. In the embodimentaccording to FIG. 10 foil 40 is provided with openings 41, through whichthe contact surfaces of fins 31 can come into mutual contact. Thesecontact surfaces are provided with adhesive layers 42, whereby the finscan be brought into direct mutual contact via these very thin adhesivelayers, as shown in FIG. 10 b. FIG. 10 also shows that the peripheraledge of opening 40 is provided with a mass 43 forming a sealing ring inorder to ensure a medium-tight connection.

FIG. 11 shows an embodiment wherein a foil 44 is provided on both sideswith an adhesive layer 45 for coupling to the contact surfaces of fins31.

In FIG. 12 the contact surfaces of fins 31 are provided with adhesivelayers 46.

FIG. 13 shows the manner in which the foil strips 48 and fin strips 49adhered thereto can be assembled to form a package such as for instancedrawn in FIG. 1.

As FIG. 13 c shows, a supply container 50 contains ten supply roll 51 onwhich are glued foil strips with fin strips thereon. One of the rolls,which is designated with reference numeral 52, contains only foilmaterial 48 without fins. The diverse strips are guided together throughthe pinch of two guide and pressure rollers 53, 54 and fed into anelectromagnetic heating device 55, whereby the hot melt present on therelevant surfaces of the foils (FIG. 11) or the contact surfaces of thefins (FIG. 12) melts, so that the desired adhesion can be realized.Inlet pressure rollers 56, 57 and 58 contribute hereto.

FIG. 13 b, which corresponds with FIG. 8, shows an embodiment in whichthe desired adhesion has been realized by pressure and temperatureincrease in device 55, 56, 57, 58, 59.

FIG. 14 shows foils 60 to which fins 61 are adhered. The foils can bepositioned by means of snap profiles 62, wherein it is noted that, dueto the respective recess 63 and the protrusion 64 co-acting therewith, alengthening of the foil is realized which, together with the elasticityof the foil, results in a certain bias. By stacking the profiles 62 aheat exchanger 1 of the type according to FIG. 1 or of other type can bemanufactured in modular manner. The pressing direction is shownsymbolically with an arrow 65. Arrow 66 designates symbolically themobility of the foil, wherein it should be understood that duringpressing as according to arrow 65 a foil is stretched and thus placedunder bias.

FIG. 15 shows the structure shown in, among others, FIG. 1, wherein theprimary and the secondary circuit follow each other.

FIG. 16 shows a variant in which two primary circuits are situatedmutually adjacently, followed by two secondary, followed by two primaryand so on.

Finally, FIG. 17 shows an alternative to the method of clampingaccording to FIG. 14. In the embodiment according to FIG. 17, each ofthe clamping blocks 62 is embodied as a generally U-shaped profile 67with an opening 68 narrowing to the outside in which is situated aroller 70 loaded by a compression spring. According to arrow 71 a foilstrip 60 can be inserted into the pinch between the lower surface 71 ofopening 68 and roller 70. While a slight pressure is exerted counter tothe spring pressure of spring 69 the leading edge of foil 60 can herebypass over the contact surface between surface 71 and roller 70. Thisarrangement takes place with some force, whereby the foil is slightlystretched until the required bias is achieved. The foil is then releasedand held fixedly in said pinch. This ensures a permanent bias.

1. Heat exchanger, comprising two sets of medium through-flow channelsthrough which two media can flow in counterflow in heat-exchangingcontact with one another; membranes separating said channels;heat-conducting fins arranged on both sides of each membrane, which finshave a main plane extending in the respective flow directions of saidmedia and a contact surface lying in the main plane of the membrane inquestion and connected thereto, wherein the contact surface of a fin onthe one side of the membrane is aligned and in thermal contact with asimilar contact surface of a fin on the other side of the membrane andwherein the contact surfaces are adhered to the membrane or to oneanother by means of an adhesive layer, the fins extending between twoadjacent membranes such that, in addition to a thermal function, thefins also have a structural function; and a housing in which themembranes with the fins are accommodated.
 2. Heat exchanger as claimedin claim 1, characterized in that corresponding contact surfaces are inthermal contact via the membrane.
 3. Heat exchanger as claimed in claim2, characterized in that the contact surfaces are adhered to themembrane by means of an adhesive layer applied to at least one contactsurface.
 4. Heat exchanger as claimed in claim 2, characterized in thatcorresponding contact surfaces are directly connected to each other viaa perforation in the membrane by means of an adhesive layer applied toat least one contact surface.
 5. Heat exchanger as claimed in claim 1,characterized in that the housing is form-retaining and the membranesare connected to the housing in manner resistant to tensile stress, suchthat the tensile stresses occurring in the membranes as a result of apressure difference between the two sets of channels can be absorbed bythe housing.
 6. Heat exchanger as claimed in claim 1, characterized inthat the membranes are biased such that, at a preselected maximumpermissible pressure difference between the two sets of mediumthrough-flow channels, the bending of the membrane between the freespace defined by the contact surfaces of the fins, i.e. the bending ofthe membrane occurring at the relevant pressure divided by the relevantmutual distance between the contact surfaces in question, amounts to amaximum of 2.5%.
 7. Heat exchanger as claimed in claim 2, characterizedin that the thermal resistance of the membrane transversely of its mainplane amounts to a maximum of 0.1 of the thermal resistance in the caseof direct contact between contact surfaces directed toward each other,and is therefore negligible.
 8. Heat exchanger as claimed in claim 1,characterized in that the thermal resistance of the membrane in its mainplane over the mutual distance between two fins adjoining in flowdirection is at least 10 times greater than in the case of fins directlycoupled to each other thermally.
 9. Heat exchanger as claimed in claim1, characterized in that the membranes consist of PET, for instancereinforced PET, that has been treated with a corona discharge and thenprovided with a primer, followed by an adhesive layer for connection tothe contact surfaces of the fins.
 10. Heat exchanger as claimed in claim1, characterized in that the membranes consist of PVC and that the finsare connected to the membranes by an ultrasonic treatment or a thermaltreatment, in combination with pressure.
 11. Heat exchanger as claimedin claim 1, characterized in that the membrane consists of afibre-reinforced material, which fibres consist for instance of glass,boron, carbon.
 12. Heat exchanger as claimed in claim 1, characterizedin that the membranes consist of a plastic in which aluminium powder isembedded.
 13. Heat exchanger as claimed in claim 1, characterized inthat the membrane or the adhesive layer applied thereto is conditionedso as to obtain a property from the group to which belong: antibacterialproperties anti-adhesion properties to repel fouling and other growthantistatic properties surface tension-changing, which conditioning canfor instance be applied by immersion or spraying with a suitable agent.14. Heat exchanger as claimed in claim 1, characterized in that themembranes protrude outside the fins such that they can be connected to aframe, for instance in order to place them under bias, or such that theprotruding membrane parts can be thermally formed into interlacing unitsand manifolds for respectively joining together and separating again thesets, of channels.
 15. Heat exchanger as claimed in claim 1,characterized in that the heat exchanger is given a modular structurewith blocks which can be releasably coupled to each other.
 16. Heatexchanger as claimed in claim 1, characterized in that the channels forma primary circuit P and a secondary circuit S and the membranes areconnected in layers ordered in the sequence P, S, P, S, P, S and so on.17. Heat exchanger as claimed in claim 1, characterized in that thechannels form a primary circuit P and a secondary circuit S and themembranes are connected in layers ordered in the sequence P, P, S, S, P,P and so on.
 18. Heat exchanger as claimed in claim 1, characterized inthat the contact surfaces of the fins have rounded peripheral edges. 19.Heat exchanger as claimed in claim 11, characterized in that the fibreshave an anisotropic heat conduction, such as carbon fibres, wherein theheat conduction is smaller in the main plane of the membrane than intransverse direction thereof.
 20. Heat exchanger as claimed in anypreceding claim, characterized in that the adhesive layer comprises ananticorrosive coating applied to at least one of the two contactsurfaces and for instance comprising a primer layer and/or an adhesivelayer extending over the whole surface of the fins and optionally themembrane.
 21. Heat exchanger as claimed in any preceding claim,characterized in that the adhesive layer is of the type which can bethermally activated and that the fins are adhered to the relevantmembrane and/or to fins located opposite thereto at the position of thecontact surfaces by heating and pressure by means of a heated pressingpunch.
 22. Heat exchanger as claimed in claims 20 and 21, characterizedin that the fins are provided on the side remote from said coating witha second coating which can withstand said heating and pressure. 23.Method for manufacturing a heat exchanger as claimed in claim 1,comprising (a) providing a number of metal strips with a general waveshape; (b) providing a number of widths of membrane material; and (c)feeding these strips and widths into a connecting device in register andin alternating relationship and mutually connecting thereof to form apackage by means of this device.